Dear Professor Phi,Do you recommend primes or zooms? Which do you prefer using and can I get "L" quality images from them since they are so relatively cheap?
Optimus Prime
Optimus Prime,
Thank you for sending me this letter. This is a very interesting topic. Primes and zooms both have some disadvantages and some very good advantages and depending on your shooting style one may work better for you compared to the other. For me, I prefer primes but let's discuss both and then you can make your own conclusion.
The first thing we will notice when comparing the two is that primes are singal focal lenses, or they don't zoom. A popular lens in the Canon world is the "normal" lens or the 50mm range. The Canon 50mm f/1.8 II can be found at online retailers in the $65-90 range. The lens has a f/1.8 aperture, which is over a stop of light faster than zooms in the same range (i.e. Canon 28-75mm f/2.8). Why is it so cheap?
The 50mm f/1.8 is mostly made of plastic for one, which is a lot cheaper to manufacture, but primes in general have a simplier layout with less elements. Because of this, they are generally less prices than "L" zooms found in the same range. At the same time, primes are usually found to have larger maximum apertures than zoom lenses for cheaper.
Keep in mind larger apertures doesn't mean better low light performer though. The wider the lens is, the easier it will be to hand hold. Imagine a 300mm f/2 vs. a 17-40mm f/4. At 17mm, the photographer's handshake is nearly negligable. Many photographers, after practice, are able to hold 17mm at shutter speeds as low as 1" but a 300mm lens will need a conserably fast shutter speed to be practical (1/focal length should be the minimum, although rules are meant to be broken 
). A wide, fast, prime could be the answer when it comes to low light photography, provided you can get close to action.
You're probably wondering, "If a prime lens is cheaper, faster (aperture), why do they even make zoom lenses?"
The answer is right in the name. Zoom lenses zoom. They have an undeniable convenience. Say you're at a wedding reception and there is action happening on stage 30 feet away but the band is 5 feet from you as well. It should be intuitive that a zoom lens should be able to cover both events without having to switch lenses. Keep in mind on the wide end of the spectrum,
primes can zoom too!
The zoom is of a trusty design that man has discovered for hundreds of years. Your legs. One of my favorite lenses is the Sigma 20mm f/1.8. It is a 20mm lens, hardly wide or long by any means, but I have found that by steping forward and back I can cover a considerable amount of subjects without having the change lenses. I get the sharpness and speed of a prime and a little excersize too. 
Zooms really aren't all that bad optically now, though. With advances in technology, the two are both good choices when it comes to photography, any kind. The biggest limitation of primes being fixed focal lenses comes on the longer end of focal lengths. Lenses like a 200mm f/2.8 vastly lose their "zooming" ability because a step forward or a step back won't mean that much of a difference. Unless you're the Flash from DC comics, you should only consider buying longer primes if you're going to be shooting something specific.
Primes provide an undeniable sharpness at affordable prices. On the wide end, they can definitely be as versatile as zooms while providing extra stops of light. On the longer end, sometimes a zoom is more preferable unless there is a specific reason you're buying it (i.e. shooting motorsports). Zooms will hit you where it hurts though, your wallet. 
Phi Dong, PhD
Professor of Photography aka The Prime Minister
i think youre talented.